This invention relates to sensing devices for measuring the flexural vibration of structural members.
Many sensors are known which are used to measure the flexural vibration of structural members. Examples of such sensors are strain gauges, pressure transducers, linear motion detectors, and other comparable devices. Most known sensors suffer from one or more disadvantages which renders each type of transducer unsuitable for a wide variety of uses. For example, many transducers depend upon relative motion between moving parts and consequently possess inherent mechanical resonances which must be accounted for, either by way of initial design considerations (e.g., mass, relative dimensions, spring constants and the like) or by the use of output signal filtering devices usually of the electrical type and incorporated into the measuring instrumentation. Other devices are sensitive to more than one mode of vibration and provide measurement signals containing both flexural vibration and rigid body vibration components. When used to measure flexural vibrations of the structural member to which the sensor is designed to be attached, additional provisions must be made to cancel out the effect of the measurement signal components corresponding to the non-flexural modes of vibration. Typically, this entails the use of another sensor which is only sensitive to the non-flexural modes of vibration, or the use of specially designed electronic measuring circuitry capable of nulling out or at least substantially filtering these undesired measurement signals. Other sensors are directional in nature and thus require extensive care in installation to ensure that the axis of maximum sensitivity is oriented along the direction of the expected flexural vibrations in the associated structural member. Still other devices are temperature sensitive and require either temperature compensation or the use of an additional temperature sensing device closely adjacent thereto to monitor the thermal environment and provide correction signals for the measurement signals produced by the sensor. Still other devices are relatively complicated to construct, test and/or calibrate; while many sensors are difficult to attach to the structural member to be monitored, frequently requiring the use of expensive attachment fixtures. Most known sensors combine several of these disadvantages.